While the present invention provides direct and/or indirect rotary position feedback by means of an optical sensing device, the current art includes the use of rotary potentiometers, such as LVDTs (Linear Variable Differential Transformers), rotary Hall effect sensors and mechanical feedback devices. Often, contact methods are employed for position feedback and cause wear of mechanical parts. In addition, it is difficult to design a pump/motor wherein a sensor can be so positioned as to read the position of the yoke/swashplate. Also, there are frequent problems in replacing and recalibrating replacement sensors.
Some prior art sensors are affected negatively by temperature, especially high temperatures that, as the pump/motor housing or casing heats up, can either ruin the sensor or at least adversely affect its precision.
The patent literature includes a large number of devices, sensors and control systems that pertain to variable displacement pump/motor assemblies and include, but are not limited to: U.S. Pat. No. 4,527,054 to White; U.S. Pat. No. 4,655,689 to Westveer et al.; U.S. Pat. No. 4,915,591 to Funke; U.S. Pat. No. 4,925,371 to Griesmar; U.S. Pat. No. 5,214,278 to Banda; U.S. Pat. No. 6,375,433 B1 to Du et al.; U.S. Pat. No. 6,623,247 B2 to Du; and U.S. Published patent application Ser. No. 2004/0115065 A1 to Du et al. However, none of these prior art devices pertains to an improved optical position sensing or to method for sensing the absolute position of a movable internal component in a variable displacement type hydraulic pump/motor assembly as set forth in the present invention.